package com.atlassian.plugin.util;
   
   import org.apache.commons.lang.StringUtils;
   
   import java.util.Comparator;
   import java.util.regex.Matcher;
   import java.util.regex.Pattern;
   
   /**
   * Compares dotted version strings of varying length. Makes a best effort with
   * other delimiters and non-numeric versions.
   * <p/>
   * For dotted decimals, comparison is as you'd expect: 0.1 is before 0.2 is before
   * 1.0 is before 2.0. This works for any number of dots.
   * <p/>
   * More complicated version numbers are compared by splitting the version strings
   * into components using the {@link #DELIMITER_PATTERN} and comparing each
   * component in order. The first difference found when comparing components
   * left-to-right is returned.
   * <p/>
   * Two numeric components (containing only digits) are compared as integers. A
   * numeric component comes after any non-numeric one. Two non-numeric components
   * are ordered by {@link String#compareToIgnoreCase(String)}.
   */
  public class VersionStringComparator implements Comparator<String>
  {
      public static final String DELIMITER_PATTERN = "[\\.-]";
      public static final String COMPONENT_PATTERN = "[\\d\\w]+";
      public static final String VALID_VERSION_PATTERN = COMPONENT_PATTERN + "(?:" + DELIMITER_PATTERN + COMPONENT_PATTERN + ")*";
      private static final Pattern START_WITH_INT_PATTERN = Pattern.compile("(^\\d+)");
  
      public static boolean isValidVersionString(final String version)
      {
          return (version != null) && version.matches(VALID_VERSION_PATTERN);
      }
  
      /**
       * Compares two version strings. If either argument is not a String,
       * this method returns 0.
       *
       * @throws IllegalArgumentException if either argument is a String,
       * but does not match {@link #VALID_VERSION_PATTERN}.
       * @see #isValidVersionString(String)
       */
      //    public int compare(Object o1, Object o2)
      //    {
      //        if (!(o1 instanceof String)) return 0;
      //        if (!(o2 instanceof String)) return 0;
      //
      //        return compare((String) o1, (String) o2);
      //    }
      /**
       * Compares two version strings using the algorithm described above.
       *
       * @return <tt>-1</tt> if version1 is before version2, <tt>1</tt> if version2 is before
       * version1, or <tt>0</tt> if the versions are equal.
       * @throws IllegalArgumentException if either argument does not match {@link #VALID_VERSION_PATTERN}.
       * @see #isValidVersionString(String)
       */
      public int compare(final String version1, final String version2)
      {
          // Get the version numbers, remove all whitespaces
          String thisVersion = "0";
          if (StringUtils.isNotEmpty(version1))
          {
              thisVersion = version1.replaceAll(" ", "");
          }
          String compareVersion = "0";
          if (StringUtils.isNotEmpty(version2))
          {
              compareVersion = version2.replaceAll(" ", "");
          }
  
          if (!thisVersion.matches(VALID_VERSION_PATTERN) || !compareVersion.matches(VALID_VERSION_PATTERN))
          {
              throw new IllegalArgumentException("Version number '" + thisVersion + "' cannot be compared to '" + compareVersion + "'");
          }
  
          // Split the version numbers
          final String[] v1 = thisVersion.split(DELIMITER_PATTERN);
          final String[] v2 = compareVersion.split(DELIMITER_PATTERN);
  
          final Comparator<String> componentComparator = new VersionStringComponentComparator();
  
          // Compare each place, until we find a difference and then return. If empty, assume zero.
          for (int i = 0; i < (v1.length > v2.length ? v1.length : v2.length); i++)
          {
              final String component1 = i >= v1.length ? "0" : v1[i];
              final String component2 = i >= v2.length ? "0" : v2[i];
  
              if (componentComparator.compare(component1, component2) != 0)
              {
                  return componentComparator.compare(component1, component2);
              }
          }
  
          return 0;
      }
  
     private class VersionStringComponentComparator implements Comparator<String>
     {
         public static final int FIRST_GREATER = 1;
         public static final int SECOND_GREATER = -1;
 
         public int compare(final String component1, final String component2)
         {
             if (component1.equalsIgnoreCase(component2))
             {
                 return 0;
             }
 
             if (isInteger(component1) && isInteger(component2))
             {
                 // both numbers -- parse and compare
                 if (Integer.parseInt(component1) > Integer.parseInt(component2))
                 {
                     return FIRST_GREATER;
                 }
                 if (Integer.parseInt(component2) > Integer.parseInt(component1))
                 {
                     return SECOND_GREATER;
                 }
                 return 0;
             }
 
             // Handles the case where we are comparing 1.5 to 1.6a
             final Integer comp1IntPart = getStartingInteger(component1);
             final Integer comp2IntPart = getStartingInteger(component2);
             if (comp1IntPart != null && comp2IntPart != null)
             {
                 if (comp1IntPart > comp2IntPart)
                 {
                     return FIRST_GREATER;
                 }
                 else if (comp2IntPart > comp1IntPart)
                 {
                     return SECOND_GREATER;
                 }
             }
 
             // 2.3-alpha < 2.3.0 and 2.3a < 2.3
             // fixes PLUG-672. We are safe to do the integer check here since above we have
             // already determined that one of the two components are not an integer and that one does not start with
             // an int that may be larger than the other component
             if (isInteger(component1))
             {
                 return FIRST_GREATER;
             }
             if (isInteger(component2))
             {
                 return SECOND_GREATER;
             }
 
             // 2.3a < 2.3b
             return component1.compareToIgnoreCase(component2);
         }
 
         private boolean isInteger(final String string)
         {
             return string.matches("\\d+");
         }
 
         private Integer getStartingInteger(final String string)
         {
             Matcher matcher = START_WITH_INT_PATTERN.matcher(string);
             if (matcher.find())
             {
                 // If we found a starting digit group then lets return it
                 return new Integer(matcher.group(1));
             }
             return null;
         }
 
     }
 }